It is often necessary to cut, shear, shred, or otherwise comminute different objects and articles for disposal purposes and, in some instances, for possible re-use. Thus, in a thermoplastic molding operation sprues, runners, and defective molded articles are commonly reduced to granular form for re-use. Another common requirement of this kind pertains to plastic barrels and other containers, and plastic pipe, which are comminuted to facilitate disposal. Yet another such application is in the reduction of used rubber tires to a form suitable for convenient and effective disposal.
One type of comminuting machine that has been generally successful in a variety of applications is disclosed, in an early version, in Schweigert et al U.S. Pat. No. 3,664,592 issued May 23, 1972; a later version of a similar machine is described in Schwarz U.S. Pat. No. 3,880,361 issued Apr. 29, 1975. In the machines disclosed in these two patents, the articles to be comminuted are fed by gravity, through an input hopper, into a comminuting chamber through which two horizontal rotary shafts extend in parallel relation to each other. A series of disc-shaped cutting blades is mounted on and rotated by each of the shafts, with each blade projecting into the space between blades on the adjacent shaft in close overlapping proximity thereto. Each blade has at least one radially projecting C-shaped cutting element affording a transverse cutting edge facing in the direction of rotation of its shaft, the two shafts being counter-rotated relative to each other. The rotating blades cut and shear articles fed into the machine, reducing them to pieces having a size suitable for convenient disposal or, in some instances for further granulation to particle sizes suitable for re-use.
Although the comminuting machines described in the aforementioned Schweigert et al and Schwarz patents are more effective and efficient than other such machines known in the art, there are nevertheless some substantial remaining problems. One major problem is the high power requirements for machines of this kind, resulting from high friction forces developed when large objects are cut and sheared and passed between the rotating blades. A related problem is frequent jamming of the machines. These problems can sometimes be alleviated by providing increased spacing between the overlapping areas of the blades on the adjacent shafts. However, this is not always effective because it tends to reduce the cutting/shearing action of the overlapping blades and is also undesirable because it may permit thin sections of the articles being comminuted to pass through the machine without adequate size reduction.
Another difficulty associated with machines of this kind results from inconsistent feeding of the articles to be comminuted into the operating chambers of the machines. Thus, for lightweight objects of substantial volume, such as plastic containers, gravity feed may be inadequate. Yet another appreciable problem in these machines results from the fact that the shearing action frequently produces long streamers from the articles being comminuted instead of the relatively small and compact pieces desired.